1. Field of the Invention
The present invention relates to an amplifier, in particular, the invention relates to an amplifier for an optical receiver.
2. Related Background Art
What is called as the PON (Passive Optical Network) communication system has became popular in the FTTH (Fiber To The Home) system. This system is necessary to convert optical signals each sent from an individual home and having a specific magnitude into an electrical signal and to amplify thus converted electrical signal. An amplifier with the function of the auto-gain control (hereafter denoted as AGC) has been also known, where the AGC circuit may adjust the gain of the amplifier based on the output thereof. A Japanese Patent Application published as JP-2010-057014A has disclosed an amplifying circuit with a level holding to stabilize a reference level provided to the input of the amplifier.